1. Field of the Invention
The present invention pertains to printed antennas made on substrates, and particularly to a printed antenna disposed on a substrate of, for example, a wireless local area network (WLAN) device.
2. Prior Art
Nowadays, wireless communication devices, such as mobile phone handsets and portable computers, are becoming more and more popular. In order for these wireless devices to communicate with one or more base stations, the wireless devices usually have to be equipped with an antenna. The characteristics of the antenna, such as efficient radiation, orientation, and frequency band, are closely connected with performance of the wireless device. At the same time, the antenna should generally also be small, light in weight, and have low radiation. There are two main kinds of antennas: one is a built-in antenna, and the other is an external antenna. In contrast to the external antenna, the size of the built-in antenna is usually smaller, and the body of the built-in antenna is less prone to be damaged.
Two kinds of built-in antennas are popularly employed: a chip antenna and a planar antenna. A printed antenna is a kind of planar antenna, and in general has the advantage of small size, low cost and simple manufacturing. With the development of the technology of wireless communications, the IEEE (The Institute of Electrical and Electronics Engineers) 802.11a standard has become one of the main technology standards of WLANs (Wireless Local Area Networks). The working frequency band of IEEE 802.11a covers the range 5.15˜5.825 GHz, and comprises 5.15˜5.25 GHz, 5.25˜5.35 GHz and 5.725˜5.825 GHz.
In order to make wireless communication devices compatible with the IEEE 802.11a standard, some new printed antennas with a working frequency band covering 5.15˜5.825 GHz have been developed. An example of such printed antenna is disclosed in Taiwan Patent No. 557608 issued on Oct. 11, 2003. The printed antenna integrates two constituent antennas into one: one operating in the frequency band of the IEEE 802.11a standard, and the other operating in the frequency band of the IEEE 802.11b standard. In short, the integrated antenna comprises two antennas that make the integrated antenna operate in a wider frequency band. However, each of the antennas has a complicated and cumbersome structure, which inflates the manufacturing cost of the integrated antenna.
In addition, many wireless communication devices need only operate on the frequency band of the IEEE 802.11a standard. Therefore, a new printed antenna with a small size and simple structure is desired to overcome the above-mentioned disadvantages of the prior art.